232
B. KIMOR: Plankton Relations of the Red Sea, Persian Gulf and Arabian Sea
continental shelves or a shallow sill as in the case of Bab-el-Mandeb, and are thus barred
from reaching the adjacent northern seas, even during the NE monsoon.
The diversity of species is, however, far more reduced in the case of the Persian Gulf,
as the shallowness of the latter environment precludes the existence of mesopelagic and
bathypelagic species which form important elements of the planktonic communities in
the Red Sea. Both seas, although completely different in their bottom topography, are
separated from the Arabian Sea by narrow straits which, by imparting to them the
character of closed sea arms, may be largely responsible for the more restricted fauna
and flora prevailing in these environments. The late THORSON (1957) in his article:
"Bottom communities", chapter 17, p. 501, states that in "large fjord areas and in Gulfs
with narrow mouths the productivity as well as the weight of the standing stock will
gradually decline with increase in distance from the open sea". He refers specifically to
the Persian Gulf where in his view the smaller weights per unit area as compared with
arctic fjords are compensated for by the faster growth rate of the animals and the much
heavier predation in the tropical area.
Although THORSON was writing of bottom communities, this may well be true with
planktonic organisms as well. Some of the examples quoted in the present survey tend
to confirm this view. Within certain systematic groups considerably fewer species than in
the adjoining ocean seem to prevail in the plankton of these closed sea arms. While this
is particularly true in the case of the Persian Gulf it also applies to the Red Sea, especially
to its northern parts, where the Gulf of Eilat and the Gulf of Suez reveal a still poorer
fauna and flora.
This bottle-neck effect apparent in the Persian Gulf, in the Red Sea as a whole, and
in the Gulf of Eilat, may well by responsible for the particular plankton features outlined
above.
On a wider regional basis significant differences seem to exist between the eastern
and the western parts of the Indian Ocean in general and between the various parts of the
Arabian Sea in particular. At times, such differences, both in biological productivity and
in species diversity, may be seen within comparatively restricted areas such as in some
parts of the Gulf of Aden or the Persian Gulf.
The question of speciation apparent in some groups of plankton organisms in the
Red Sea stimulates further research. While the hydrographic conditions in the Red Sea
seem to favour the evolution of endemic species, or species considered to have had their
origin in this sea, the actual boundaries of distribution of such species may be much wider,
as proved in a number of cases. Much more work is needed for firm and absolute conclusions, and the results so far available from the HOE regarding such plankton relations
seem to have prepared the road and stimulated the interest for the work still to be done.
B. KIMOR: Plankton Relations of the Red Sea, Persian Gulf and Arabian Sea
continental shelves or a shallow sill as in the case of Bab-el-Mandeb, and are thus barred
from reaching the adjacent northern seas, even during the NE monsoon.
The diversity of species is, however, far more reduced in the case of the Persian Gulf,
as the shallowness of the latter environment precludes the existence of mesopelagic and
bathypelagic species which form important elements of the planktonic communities in
the Red Sea. Both seas, although completely different in their bottom topography, are
separated from the Arabian Sea by narrow straits which, by imparting to them the
character of closed sea arms, may be largely responsible for the more restricted fauna
and flora prevailing in these environments. The late THORSON (1957) in his article:
"Bottom communities", chapter 17, p. 501, states that in "large fjord areas and in Gulfs
with narrow mouths the productivity as well as the weight of the standing stock will
gradually decline with increase in distance from the open sea". He refers specifically to
the Persian Gulf where in his view the smaller weights per unit area as compared with
arctic fjords are compensated for by the faster growth rate of the animals and the much
heavier predation in the tropical area.
Although THORSON was writing of bottom communities, this may well be true with
planktonic organisms as well. Some of the examples quoted in the present survey tend
to confirm this view. Within certain systematic groups considerably fewer species than in
the adjoining ocean seem to prevail in the plankton of these closed sea arms. While this
is particularly true in the case of the Persian Gulf it also applies to the Red Sea, especially
to its northern parts, where the Gulf of Eilat and the Gulf of Suez reveal a still poorer
fauna and flora.
This bottle-neck effect apparent in the Persian Gulf, in the Red Sea as a whole, and
in the Gulf of Eilat, may well by responsible for the particular plankton features outlined
above.
On a wider regional basis significant differences seem to exist between the eastern
and the western parts of the Indian Ocean in general and between the various parts of the
Arabian Sea in particular. At times, such differences, both in biological productivity and
in species diversity, may be seen within comparatively restricted areas such as in some
parts of the Gulf of Aden or the Persian Gulf.
The question of speciation apparent in some groups of plankton organisms in the
Red Sea stimulates further research. While the hydrographic conditions in the Red Sea
seem to favour the evolution of endemic species, or species considered to have had their
origin in this sea, the actual boundaries of distribution of such species may be much wider,
as proved in a number of cases. Much more work is needed for firm and absolute conclusions, and the results so far available from the HOE regarding such plankton relations
seem to have prepared the road and stimulated the interest for the work still to be done.